The goal of this career development award is for Dr. Philip A. Chan to acquire the training and experience necessary to become an independent clinical investigator. The career goals of this proposal are to gain expertise in the field of HIV-oriented molecular epidemiology including familiarity with biostatistics and study design, to become skilled using molecular phylogenetics to study HIV transmission patterns and population dynamics, to acquire experience in HIV behavior and prevention sciences, and to receive proper training in the Responsible Conduct of Research including ethical practices. The number of Human Immunodeficiency Virus (HIV) infected individuals continues to increase in the United States, propagated by transmission in social networks among high-risk groups. Identification of networks within which HIV transmission occurs can lead to targeted screening and effective prevention interventions. Current HIV epidemiologic contact tracing programs implemented by public health departments are often limited by reporting and recall bias secondary to the lag time between infection and diagnosis as well as the reluctance of HIV-infected individuals to report partners. This research proposal integrates molecular epidemiology and public health programs to identify transmission networks and develop behavior assessment and intervention tools. In collaboration with other major academic centers in Rhode Island and the Department of Health, molecular epidemiology will be used to enhance contact tracing programs and develop future targeted prevention strategies. The objectives of the research are to: 1) Identify transmission networks among HIV- infected individuals using molecular phylogenetic approaches; 2) Determine risk factors and characteristics associated with transmission networks that may be targeted for interventions; and 3) Identify contacts of individuals forming transmission networks to diagnose HIV-infected yet unaware cases, characterize risk behaviors, and assess acceptability of novel prevention interventions. This research will allow a comprehensive investigation of HIV epidemiology and development of an effective public health model that can be implemented elsewhere. During the course of this award, Dr. Chan will be mentored by experts from Brown University in the field of molecular genetics and HIV epidemiology including Dr. Rami Kantor (primary mentor) and Dr. Kenneth Mayer.